Are you using EC2 - and maybe even ElastiCache? Are you sure you are really leveraging the Cache? In this blog we talk about a SaaS company that figured out that using a 3rd party client library to access the cache had a bug that resulted in not putting any objects in the cache at all. This resulted in high CPU processing on the servers as all their documents needed to be processed for each request instead of pulling them from the cache leading to frustrated end users and higher operational costs to run their SaaS software on EC2